Has anyone made a 40k Space Marine race yet? I am thinking of trying to convert Deathwatch. Thank you in advanced.

I'm not aware of any specific Space Marine Races yet, however you could take the Dark Heresy races (found in the master resources) or Core Book's archetypes and use the super rules in the Core Book. Hope that helps!

Yeah you might need to up their power level and equipment from the standard creation rules, but using superheroes rules sounds like a great idea and maybe add boost dice to represent unnatural strength and toughness.

I was working on a 40k game using the Genesys book, I was going to use the Laborer Archetype for the space marine statline. All of the weapons, armor and gear you need are in the book though. I came up with rules for almost any space marine weapon I could think of!

I was working on something for this actually. Nowhere near finished, but here's how far I got before my development semi-hiatus started due to real life stuff getting in the way.

Take a look. Might not be to everyone's taste, and it's blatantly missing a lot of content (like an armoury), but might be some solid inspiration at least. It was made specifically for high level Inquisitorial parties, so it requires a big chunk of extra XP granted by the GM. You might look at taking a different approach if running a purely Marine focused game; could adjust the narrative scale and dial the stats back a notch.

This is made as an expansion for my Dark Heresy setting rules, so if you haven't read those a lot of this won't make sense.